The present invention relates to methods of producing animal feed from food waste by providing a dry, pelletized, fibrous organic material. Specifically, the invention relates to methods of thickening/dewatering solids that contain substantial amounts of moisture, e.g. ground food waste. More particularly, the invention relates to methods for thickening ground food waste as a water based slurry utilizing synthetic organic flocculants usable as animal feed additives. The invention also relates to methods of treatment of the separated liquid phase (supernatant or filtrate) resulting from thickening water based slurries.
It is known in the art that an extrusion process that is a part of the food waste pelletization and drying technology cannot be provided when the liquid-solids admixture contains substantial amounts of liquid, e.g. water. U.S. Pat. No. 5,596,815 (Rice et al.) describes a method for moisture reduction by adding a dry material. This dry material adds to the cost of the process.
U.S. Pat. No. 5,908,634 presents an animal feed in powder or granular form containing molasses and 10 to 60% of bentonite and zeolite, which is added as a dehydrating agent, and causes the delayed release of nitrogen. Hydrated lime may be added as a source of calcium, to improve pellet quality. The addition of bentonite and zeolite as dehydrating agents require curing times of up to 12 hours, which is a drawback of the invention. Also, addition of the dehydrating agent in amounts of up to 60% diminishes the nutrient value of the animal feed.
U.S. Pat. No. 5,955,023 describes a method of forming a composite particle product from lignin-cellulose material bonded together with water insoluble lignin (2-40% by weight) and a binding agent. The mixture is then heated and compressed to promote bending and cross-linking between the lignin binder and the lignin-cellulose material. Lignin functions as the primary adhesive for the product, and forming the particleboard product from the lignin bonding mixture. The drawback of the method is a necessity to use heat (between 100 and 240xc2x0 C. for 1 to 60 seconds) to bind lignin with the cellulose material. Also, the initial lignin-cellulose material has to have a moisture content of about 30% or less, and water-insoluble lignin has to be dissolved in an organic solvent and then be evaporated.
U.S. Pat. No. 5,958,233 reveals a process and apparatus for dewatering aqueous solids residual after fermentation and distillation, such as corn stillage. The feed stream of aqueous solids slurry is fractionated into two or more sub-streams in such a way that one of the sub-streams contains predominately heavy particulate solids and has substantially improved free-draining characteristics. A second sub-stream contains lighter particles, entrained fines of the heavy particles, and a major portion of the liquid from the feed stream. The free-draining sub-stream is dewatered using a device such as a screen centrifuge or a screw press, both of which produce a cake of relatively high solids content. The remaining liquid from the feed stream is concentrated in an evaporator, before being mixed with the dewatered solids, which may be dried to produce an animal feed. The drawback of the process is the loss of nutrients in the second sub-stream containing lighter particles to be potential animal feed unless the second sub-stream containing lighter particles along with the liquid phase separated from the free-draining sub-stream are evaporated; evaporation of the liquid phases is not economical. Another drawback of the process is that it is limited to a fat free material, such as corn stillage, and the method of dewatering of the free-draining sub-stream cannot be used for a material rich in fat unless the free-draining characteristics are substantially improved.
U.S. Pat. No. 5,976,594 discusses a process for turning food waste into animal feed including agitating the ground food waste in a blending tank so that the food waste is suspended. A production system includes a series of pipes and tanks through which food waste is processed and dehydrated so that the food waste is ultimately converted into animal feed. Dry feed stock is added as dehydrated material, and the mixture is then converted into moist pellets that are then dried and packaged for further distribution. The shortcoming of the process is inadequate dewatering of the food waste, resulting in large amounts of dehydrating agent added, which makes the animal feed not economical.
U.S. Pat. Nos. 6,030,565 and No. 6,194,065 describe an agglomerate and a process for its manufacture by providing a dry, particulated, fibrous organic material that is mixed with a powdered mineral, thus resulting in the first mixture. A binding agent is added to the first mixture, in order to obtain a second mixture. The agglomeration of the second mixture in an agglomeration dish and drying the agglomerate results in a desired dried state. The drawbacks of the process are that processing the fibrous organic material in a heated screw press, as well as the addition of a binding agent, add to the cost of the final product. Also, the agglomeration process requires the addition of a binding agent from the group consisting of chemical adhesives, resins and starches, and these materials are not considered animal feed.
U.S. Pat. No. 6,106,673 provides a process and system for the separation of a fermentation process by-product into its constituent components. The process requires heating of a mixture containing the by-product to separate the oil from a base component of the by-product. Oil separation is followed by recovering the base product, the oil, and, possibly, other substances such as molasses from the mixture by evaporation (at a temperature between 140xc2x0 F. to 250xc2x0 F.). The drawback of that process is excess energy consumption.
U.S. Pat. No. 6,132,625 provides a method that can be used to clarify substantially aqueous streams and optionally separate biosolids, especially proteins, from food processing operations. The method comprises the contact of an aqueous stream comprising biosolids with an anionic, inorganic, colloidal material selected from the group of polysilicate microgels, and an organic polymer (two cationic flocculants with a low and high molecular weight), to flocculate the biosolids. A process is provided which can be used to clarify substantially aqueous streams and optionally separate biosolids, especially proteins, from food processing operations, which comprises contacting an aqueous stream comprising biosolids with an anionic inorganic colloid and an organic polymer, to flocculate the biosolids. A drawback of the invention is that it is limited to a substantially aqueous stream containing biosolids, especially protein. A quality animal feed will also contain fats in an optimum ratio to proteins. If such an aqueous stream is separated from the food waste, it may contain highly concentrated and hardly treatable organic material that could not be treated using only the synthetic organic flocculants.
U.S. Pat. No. 5,891,254 describes a method for purifying an aqueous sugar solution by a hydrolyzed polyacrylamide. The invention describes clarification of sugar juice, related to the treatment of the supernatant in the process modification described above. This reference considers sludge to be a disposable residue, while the clear juice is the ultimate product. The polymer binding solids is removed with waste sludge, and its effect on the final product (sugar juice) is negligible. The major drawback of the invention is that it is limited to sugar juice production, and the sludge, when considered an animal feed, is processed to provide a necessary fat-to-protein ratio that is not a subject of the patent. Another drawback of the invention is that it is limited to a relatively clear liquid, such as sugar juice containing primarily carbohydrates. Such a liquid is treated with a hydrolyzed polymer, and the method cannot be used for treating fat and protein contaminated liquid unless an organic material destruction process is implemented.
U.S. Pat. No. 5,759,568 describes a method for producing animal foodstuff from waste, and is based on addition of bentonite and a polymer to the waste stream. The reference describes the flow subject to treatment as a combination of, at least, three aqueous streams, so that the final stream can be very diluted. This is confirmed by the use of a flotation method for solids-water separation, resulting in the discharge of the effluent to the sewer system. A substantial drawback of the invention is that the flotation process results in separated solids containing abundant moisture, and the effluent containing residual suspended solids. The reference does not disclose destruction of highly concentrated organic material resulting from separation of the solid containing both the fats and the proteins, so it is limited to the diluted streams. The reference assumes the use of filter presses (belt presses) for sludge dewatering that significantly adds to the cost of the process. Nonetheless, the filtrate will contain abundant residual dissolved and colloidal organic material that has to be separated and treated using a combination of the destruction and separation methods.
U.S. Pat. No. 6,132,625 assumes the use of a combination of inorganic and organic coagulation-flocculation means for phase separation. The use of inorganic coagulants makes the ultimate product unusable as an animal food additive, resulting in the invention being not applicable for the purpose of making animal feed from the food wastes.
U.S. Pat. No. 4,728,517 assumes production of animal feed from float sludge and from activated sludge. Bulking agents, e.g. wood chips and the like, added to remove fats as well as coagulation and flocculation agents are considered components of ultimate animal food. In this reference, the liquid phase (supernatant) is not removed from the system and is added to the batch. Thus, that liquid is evaporated, thereby inefficiently consuming substantial amounts of energy.
It is an object of the present invention to provide a continuous process comprising shredding food waste containing fats without fat emulsification, followed by thickening of shredded (ground) food waste using an appropriate synthetic organic flocculant approved as an animal feed additive. The thickened food waste is preferably a low moisture product subject to extruding (pelletization) followed by pellet excess liquid evaporation. The liquid phase separated in the thickening process is then treated, thus providing a high purity final effluent usable for recycling, and excess sludge usable as animal feed additive.
A further object of the present invention is to provide a continuous process of mixing the ground food waste with an appropriate synthetic organic flocculant, followed by thickening.
A further object of the present invention is to provide a process for treatment of the liquid phase resulting from the thickening process by a combination of the appropriate phase separation processes and destruction and/or adsorption of the organic material.
In accordance with the above-noted objectives, the present invention is a system and process for producing animal feed from food waste comprising shredding (grinding) of the food waste, followed by thickening of ground food waste using an appropriate synthetic organic flocculant approved for animal food additives, thus resulting in a low moisture product, and treating the liquid phase by a method and apparatus providing high purity final effluent and excess sludge usable as animal food additive.